Comparison ALTEK SC-LH3-30 vs ALTEK AC-VG-25

— Open. Open collectors are called collectors that work without additional pressure in the water circulation system. Usually, such a device is equipped with a tank in the upper part, into which a supply of water is poured; after that, the water by gravity flows to the tap. At first glance, open systems are not very convenient: they need to be placed higher (and the pressure will depend on the height difference between the collector and the water tap), while it is necessary to think over the way to fill the tank (bring a hose with a pump to it), and the purpose of such devices is limited domestic hot water supply and heating pools. On the other hand, such collectors are extremely simple, inexpensive, do not require a connection to the mains and can work even in the absence of electricity (as long as there is water in the tank).

Another design option is devices without a tank powered by a circulation pump. However, they are less common, mainly among models for heating pools (see "Suitable for").

— Closed. Closed collectors require high-pressure operation (about 5–6 bar) and are designed for direct integration into the DHW supply system. In this case, the indirect principle of operation is usually used for heating — the transfer of heat from the water in the collector to the water in the DHW system through a special heat exchanger.

Such devices are noticeably more complicated...and expensive than open ones. At the same time, they are more versatile and efficient; they can be used for domestic hot water and heating. In addition, you can install the heater at any height. It does not affect the pressure in the system, unlike open design.

The method of installation of the collector.

It is worth noting that all solar collectors are designed for installation at an angle to the horizon. It is due to this that it is possible to achieve the angle of the sun's rays will be as close as possible to the perpendicular — and the efficiency of the device will be close to maximum. Therefore, both horizontal and inclined models are essentially installed in the same position — inclined; the difference between these options is that what serves as a support for the collector. See the relevant paragraphs for details.

— Inclined. Collectors are designed for installation on a special frame. Thanks to this frame, the absorbing surface is located at the right angle to the horizon, while the frame itself is designed for installation on a flat horizontal surface. If you plan to place the collector on such a surface — for example, on a flat roof or the ground next to the house — it is worth paying attention to inclined models.

— Horizontal. Horizontal devices are devices that are not equipped with stands and, in general, are not designed to use stands. Such collectors are laid directly on the roof surface, while the required angle of inclination is ensured solely by the slope of the surface. Accordingly, the main scope of horizontal models are houses with sloping roofs, where it is impossible to install an inclined collector. The di...sadvantage of this option is that the angle of the device directly depends on the angle of the roof.

— Universal. Collectors that can be installed both horizontally and inclined way. For more information about these options, see the corresponding paragraphs, and their combination in one model allows the user to choose the best option, depending on the situation. However, such versatility is not cheap, and it is rarely required — a solar collector is usually purchased based on a strictly defined installation site, and with the choice of a specialized option (inclined or horizontal), usually, there are no problems. As a result, such models are extremely rare. Also, note that the frame may not be included and will need to be purchased separately.

The main application the solar collector is designed for. It is highly undesirable to deviate from these recommendations: the specific features of the design and operation depend on the purpose, and in the “non-native” mode, the device will at best be inefficient, and at worst it may fail and even lead to accidents.

— DHW. Application in domestic hot water supply systems is a classic option, the vast majority of modern solar collectors are made for. The specific method of embedding in the DHW system may be different: in particular, open models use direct water heating, and closed models use indirect heating (for more details, see "Loop system"). Anyway, solar heating can be very handy for providing hot water. It can play both an auxiliary role (to save energy during the main heating or as a backup in case the hot water is turned off), and the main one (for example, in a country cottage or other similar place where there is no hot water initially).

— Heating and DHW. Devices designed for use both for hot water supply and heating. For DHW, see the relevant paragraph for more details; however, not everything described there is true for this category. For the collector to be effectively integrated into the heating system, it must meet certain additional requirements. First of all, such an application is allowed only for closed devices (see "Loop system") — the heating circuit operates unde...r fairly high pressure and forced circulation, an open operation scheme is not applicable here. Secondly, the “heating” collector must allow year-round use (see “More features”) — after all, the heating issue is most acute in the cold season, and not all models can work at low outdoor temperatures.

— Swimming pool heating. This category includes high-performance solar collectors that can be used for heating water in the pool, as well as for other purposes that require a constant supply of large amounts of hot water — for example, the operation of underfloor heating systems or a set of bathtubs. Of course, they can also be used in a more traditional format — for example, for DHW systems; however, the described tasks associated with large consumption of heated water remain the main specialization.

The material from which the absorber is made. It is a layer that absorbs solar energy. It is the main part of the collector; the general specs of the device largely depend on its design.

In most modern models, regardless of type, the absorber is made of copper with a special coating. This metal has a high thermal conductivity and effectively transfers heat to the heating medium. And the coating is used to improve the absorption of sunlight, reduce its reflection and, accordingly, achieve good efficiency indicators.

Another option found in solar collectors is aluminium. It is somewhat cheaper than copper and weighs less, but it is inferior to copper in terms of thermal conductivity and performance.

The total area of the absorbing surface of the collector. For kits with multiple collectors (see "Number of collectors"), the area for one device is indicated.

Note that the meaning of this parameter depends on the type of collector (see the relevant paragraph). In flat devices, we are talking about the working area — the size of the surface that is exposed to sunlight. In tubular models (vacuum, thermosiphon), where tubes play the role of an absorber, the total surface area of the tubes is taken into account — including that which is “in the shade” during operation and is not heated by the sun. Special reflectors can be used to overcome this problem.

All of the above means that only collectors of the same type and similar design can be compared with each other in terms of absorber area. If we talk about such a comparison, then a large area, on the one hand, provides greater efficiency and heating speed, and, on the other hand, it accordingly affects the dimensions of the device and the amount of space required for its installation. Thus, the total area of a flat collector approximately corresponds to the area of the working surface; it is slightly larger, but this difference is small. But in tubular models, there is a paradox when the total area is less than the absorber area.

Collector aperture area; in sets of several devices (see "Number of collectors") is indicated for one collector.

The aperture area is, in fact, the working area of the device: the size of the space directly illuminated by the sun. In flat models (see "Type") this size corresponds to the size of the glass surface on the front side of the collector; in this case, the aperture area is usually either equal to the area of the absorber (see the relevant paragraph) or slightly less (because the edges of the collector can cover the edges of the absorbing surface. But in tubular collectors (vacuum, thermosiphon), the aperture area can be measured in different ways, depending on the presence of a reflector. If it is present, the working area is equal to the absorber area, since the tubes are irradiated from all sides. If a reflector is not provided, then the aperture area is taken as the sum of the projection areas of all tubes; projection length at this corresponds to the length of the tube, the width to the inner diameter of the glass bulb or the outer diameter of the inner tube, depending on the design.

The aperture area is one of the most important parameters for modern solar collectors; many performance specs depend on it. At the same time, by recalculating these specs per 1 m2 of the aperture area, one can compare different models (including those belonging to different types) with each other.

The total area of the collector. If there are several collectors in the kit, this indicator is given for one device.

The total area determines, first of all, the dimensions of the collector and the amount of space required for its installation. In this case, if we are talking about horizontal placement (see "Mounting"), then the total area of the collector will correspond to the area of the space that it will occupy after installation. But with inclined installation, the base of the entire structure occupies a slightly smaller area — this is due to the specifics of the installation.

It is worth talking about the total area and aperture area. The practical specs of a solar collector are determined primarily by its aperture area, for more details on it, see the relevant paragraph. At the same time, in flat models (see “Type”), the aperture area will inevitably be less than the total. But in tubular models, it can be the other way around — in some cases, the aperture surface area of all tubes may exceed the total area of the device itself. There is nothing strange in this, such a phenomenon is associated with the geometric features of the design.

The total number of tubes provided in the design of the solar collector (vacuum or thermosyphon, see "Type").

This parameter largely depends on the area of the device: for a large collector, more tubes are required. However, there is no hard dependence here. Devices of similar size may differ in the number of tubes. In general, this parameter is quite specific, it is used in some formulas for calculating the required collector power.

The maximum pressure of the heating medium for which the collector is designed. This parameter is indicated only for closed models (see "Loop system") — by definition, open models operate at atmospheric pressure.

The maximum pressure allowed for the collector must not be lower than the operating pressure in the heating system (DHW, heating, etc.) to which it is planned to be connected. And ideally, you should choose a device with a pressure margin of at least 15 – 20% — this will give an additional guarantee in case of various failures and malfunctions.